The following is the explanation that i found from MANHATTAN GMAT:
Can someone explain better ?

It is tempting to view the information in the question as establishing a pattern as follows:

Green, Yellow, Red, Green, Yellow, Red, . . .

However, consider that the following non-pattern is also possible:

Green, Yellow, Red, Green, Green, Green, Green . . .

(1) INSUFFICIENT: This tells us that the 18th tile is Green or Red but this tells us nothing about the 24th tile. Statement (1) alone is NOT sufficient.

(2) INSUFFICIENT: This tells us that the 19th tile is Yellow or Red but this tells us nothing about the 24th tile. Statement (2) alone is NOT sufficient.

(1) AND (2) INSUFFICIENT: Together, the statements yield the following possibilities for the 18th and 19th tiles:

GY, GR, RY, or RR

However, only GY adheres to the rules given in the question. Thus, we know that tile 18 is green and tile 19 is yellow. However, this does not help us to determine the color of the next tile, much less tile 24 (the one asked in the question). For example, the next tile (tile 20) could be green or red. Thus, the statements taken together are still not sufficient.

The correct answer is E.

Anurag@Gurome wrote:

karthikpandian19 wrote:In a single row of yellow, green and red colored tiles, every red tile is preceded immediately by a yellow tile and every yellow tile is preceded immediately by a green tile. What color is the 24th tile in the row?

(1) The 18th tile in the row is not yellow.

(2) The 19th tile in the row is not green.

Note that there is no restriction about which color can precede any green tile. Thus green may appear anywhere in the series. Now looking at the statements we can say that the answer will be E, because there is no definite regularity in the series or we can go for a detailed analysis.

(1) The 18th tile in the row is not yellow.
Thus it may be either red or green. Hence the color of 24th tile may depend on the color of this 18th tile; NOT sufficient.

(2) The 19th tile in the row is not Green.
Thus it may be either red or Yellow. Hence the color of 24th tile may depend on the color of this 19th tile; NOT sufficient.

Combining (1) and (2) together, from statement (1), 18th is either red or green which means 19th is either Green or Yellow. But from statement (2), 19th tile is either Red or Yellow or Green. Combining these two, we get that 19th tile is either Yellow or Green; NOT sufficient.

The correct answer is E.

Hello Sir,

I didnt get this. From statement 1, it is clear that 19th is either green or yellow.
Statement 2 says that 19th is not green. So combining these 2 cant we say that 19th is yellow
Please help

Regards,
Vishal

vishal.pathak wrote:
I didnt get this. From statement 1, it is clear that 19th is either green or yellow.
Statement 2 says that 19th is not green. So combining these 2 cant we say that 19th is yellow
Please help

The pattern is like this
G->Y->R

We dont know which color preceds green and which comes after red

St 1- The 18th tile in the row is not yellow.
18th tile=> red or green
we dont know which color would follow red
19th tile=> Green,red or yellow
Not sufficient

St-2- The 19th tile in the row is not green.
19th tile=> red or yellow
Not Sufficient

Combine the two sts
19th tile=> red or yellow
Not Sufficient

Option E